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Electronic-state modulation utilizing the electrostatic properties and dynamics of hydrogen-bonding (H-bonding) protons is an effective strategy for realizing novel electron–proton-coupled functionalities. However, material developments based on this strategy have been limited to a few π-electron systems; thus, the realization of solid-state electron–proton-coupled functionalities is challenging. Here, we successfully synthesized new crystals based on nickel catecholdithiolene complexes, which are d/π-electron systems with H-bonds, exhibiting various deprotonation/oxidation states brought about via solution processes. In these crystals, unique three-dimensional framework or two-dimensional sheet structures are formed by intermolecular H-bonds between the complexes, including anionic [O–H⋯O]− H-bonds (dO⋯O ∼ 2.59 A), which were advantageous for proton transfer in solid states. Importantly, detailed analyses revealed that the nickel complexes in the crystals were in various oxidation/deprotonation states. Accordingly, the magnetic properties changed from paramagnetic to non-magnetic with the oxidation of the complexes through proton-coupled electron transfer in solution processes. Density functional theory calculations revealed that the d/π electronic states of the nickel complexes in each crystal are significantly modulated depending on the deprotonation/oxidation states. We propose a possible mechanism for the oxidation-coupled deprotonation of the nickel complex, where various oxidation/deprotonation states can be obtained as crystals and controlled by recrystallization conditions, which is realized by the characteristic d/π-conjugation property and (de)protonation/redox activity of the nickel catecholdithiolene complex. The findings provide a further possibility to construct d/π-electron–proton-coupled collective functionalities based on this complex, together with significant insights for exploring novel electron–proton-coupled functionalities in the solid state.

We investigated the multiscale characters of the crystal structure of the oxynitride perovskite LaTiO2N. While X-ray diffraction results identified the average structure as being centrosymmetric, we detected a signature of unknown structural deformation. By viewing the local structure, we unveiled the formation of a polar structure at the nanoscale.

The relationship between the magnetic interaction and photoinduced dynamics in antiferromagnetic perovskites is investigated in this study. In La${}_{1/3}$Sr${}_{2/3}$FeO${}_{3}$ thin films, commensurate spin ordering is accompanied by charge disproportionation, whereas SrFeO${}_{3}$ thin films show incommensurate helical antiferromagnetic spin ordering due to increased ferromagnetic coupling compared to La${}_{1/3}$Sr${}_{2/3}$FeO${}_{3}$. To understand the photoinduced spin dynamics in these materials, we investigate the spin ordering through time-resolved resonant soft X-ray scattering. In La${}_{1/3}$Sr${}_{2/3}$FeO${}_{3}$, ultrafast quenching of the magnetic ordering within 130 fs through a nonthermal process is observed, triggered by charge transfer between the Fe atoms. We compare this to the photoinduced dynamics of the helical magnetic ordering of SrFeO${}_{3}$. We find that the change in the magnetic coupling through optically induced charge transfer can offer an even more efficient channel for spin-order manipulation., 7 pages, 5 figures

Nanostructure-induced L10-ordering of twinned single-crystals in CoPt ferromagnetic nanowires on Si/SiO2 substrates is demonstrated, where nanostructure-induced L10-ordering is driven by ultrasmall 10 nm-scale curvature radii of the nanowires.

Purely organic crystals, κ-X3(Cat-EDT-TTF)2 [X = H or D, Cat-EDT-TTF = catechol-fused tetrathiafulvalene], are a new type of molecular conductor with hydrogen dynamics. In this work, hydrostatic pressure effects on these materials were investigated in terms of the electrical resistivity and crystal structure. The results indicate that the pressure induces and promotes hydrogen (deuterium) localization in the hydrogen bond, in contrast to the case of the conventional hydrogen-bonded materials (where pressure prevents hydrogen localization), and consequently leads to a significant change in the electrical conducting properties (i.e., the occurrence of a semiconductor–insulator transition). Therefore, we have successfully found a new type of pressure-induced phase transition where the cooperation of the hydrogen dynamics and π-electron interactions plays a crucial role.

We have designed and synthesized a novel metal dithiolene complex with hydrogen-bonding (H-bonding) ability, [Au(catdt)2]− (catdt: catechol-4,5-dithiolate) and successfully constructed [Au(catdt)2]−-based three-dimensional (3D) anionic molecular frameworks in two kinds of salts, (Ph4P)[Au(catdt)2]·0.5H2O (3a) and (Ph4P)[Au(catdt)2]·Et2O·n(solv) (3b; solv = Et2O and/or acetone). To our knowledge, these are the first examples of the 3D molecular frameworks based on H-bonded metal dithiolene complexes. Importantly, these frameworks are constructed through 3D intermolecular H-bonds between [Au(catdt)2]− molecules, and have tubular channels occupied by large Ph4P+ cations, where multiple cation–anion short contacts are formed to stabilize the 3D framework structures. Furthermore, in addition to 3a and 3b with 3D frameworks, we have obtained (Ph4P)[Au(catdt)2]·2THF (3c) having a 2D layered structure. A detailed comparison of the structures of these compounds reveals that the included solvent molecules play an important role in regulating the intermolecular interactions and assembled structures. Interestingly, we have found that, due to the differences in the H-bonding ability and molecular size of H2O and Et2O, the wall structures of the 3D frameworks in 3a without voids and 3b with voids are qualitatively different.

L10-ordered CoPt with a large coercivity (H c) of 13 kOe was demonstrated on Si/SiO2 substrates by hydrogen annealing. Equiatomic 11.2 nm thick (Co/Pt)4 multilayer thin films were fabricated by electron-beam evaporation and were annealed at 500 °C–900 °C for 10–90 min under an Ar/H2 mixed gas atmosphere. The annealing temperature and time dependences of the crystal structures, magnetic properties, and surface morphologies of the films were systematically analyzed based on the experimental results obtained from grazing incidence X-ray diffraction (GI-XRD), vibrating sample magnetometer, and scanning electron microscope, respectively. Hydrogen annealing effectively promoted the out-of-plane c-axis orientation of L10-ordered CoPt compared to the vacuum annealing according to the GI-XRD patterns. A maximum H c of 13.3 kOe was obtained in L10-ordered CoPt with angular-outlined isolated grains by hydrogen annealing at 800 °C for 60 min, where the c-axis of L10-ordered CoPt was randomly distributed.

Anthracene, a simple planar building block for organic semiconductors, shows strong intermolecular interactions and exhibits strong blue fluorescence. Thus, its derivatives have a great potential to integrate considerable charge carrier mobility and strong emission within a molecule. Here, we systematically studied the influence of alkyl chain length on the crystal structures, thermal properties, photophysical characteristics, electrochemical behaviors, and mobilities for a series of 2,6-di(4-alkyl-phenyl)anthracenes (Cn-Ph-Ants, where n represents the alkyl chain length). Among them, Cn-Ph-Ants (n = 0, 1, 2, and 3) display similar layered herringbone (LHB) packing motifs, which facilitate two-dimensional charge transport and thereby enables high-performance organic field-effect transistors (OFETs). All Cn-Ph-Ants exhibit similar work functions and show strong blue fluorescence with photoluminescence quantum yields (PLQY) of approximately 40% in toluene. In addition, the absolute powder PLQYs of C0-, C2-, C3-, C4-, and C6-Ph-Ants are 24.6, 8.2, 5.7, 10.9, and 8.6%, respectively. Note that the alkyl chain length shows a significant effect on the charge mobilities of Cn-Ph-Ants. Our newly synthesized C1-, C3-, and C4-Ph-Ants show hole mobilities of up to 2.40, 1.34, and 1.00 cm2 V-1 s-1, respectively, with mobilities of 3.40, 1.57, and 0.82 cm2 V-1 s-1 for C0-, C2-, and C6-Ph-Ants, indicating an increasing tendency of mobility with shorter alkyl chain length. This feature is related to the microstructures of the thin films, which reveal the enhanced film order, crystallinity, and grain size with a decrease in the alkyl chain length. Moreover, we theoretically analyze the intermolecular transfer integrals of HOMOs, which increase at T-shaped contacts as the alkyl chain length decreases, which improves the intermolecular charge transport properties, leading to the increases in mobility. Interestingly, the anisotropy of the transfer integral tends to decrease upon substitution with longer alkyl chains, suggesting that alkyl chain adjustments may facilitate isotropic charge transport property in 2,6-alkylated anthracenes.

Magnetic excitations in layered electride ${\mathrm{Y}}_{2}\mathrm{C}$ have been found by inelastic neutron scattering. We have observed weak but clear magnetic scattering around the wave number $Q=0$, but no magnetic order down to the lowest temperature measured (7 K). The imaginary part of the dynamical susceptibility deduced is well described by the Lorentz function of energy $E$ for each momentum $Q$. The width $\mathrm{\ensuremath{\Gamma}}(Q)$ of the Lorentzian is proportional to $Q({Q}^{2}+{\ensuremath{\kappa}}^{2})$ with ${\ensuremath{\kappa}}^{\ensuremath{-}1}\ensuremath{\sim}4\phantom{\rule{4pt}{0ex}}\AA{}$ at $T=7$ K. We have also found that with increasing $Q$ the magnetic form factor decays faster than that of a $4d$ electron in a single Y atom, which indicates a more extended magnetic moment in ${\mathrm{Y}}_{2}\mathrm{C}$. These results provide experimental evidence that the itinerant magnetism in ${\mathrm{Y}}_{2}\mathrm{C}$ originates from the anionic electrons that reside in the interlayers. The Curie-Weiss-like behavior of the magnetic susceptibility reported in ${\mathrm{Y}}_{2}\mathrm{C}$ is ascribed to the mode coupling effects of spin fluctuations.

High critical temperature (Tc) superconductivity is generally considered to result from a fluctuation-mediated Cooper-pairing derived from a parent phase. The question of what type of fluctuation forms in materials thus plays a key role in understanding the mechanism of superconductivity. The iron-based superconductor LaFeAsO1-xHx possesses bipartite magnetic parent phases with centrosymmetric (x ~ 0) and non-centrosymmetric (x ~ 0.5) structures. The latter is an intriguing polar-metal phase induced by temperature and carrier doping. Here, we investigate average and local structures of LaFeAsO1-xHx using X-ray diffraction and extended X-ray absorption fine-structure measurements. We found lattice C4 symmetry breaking far above the structural transition temperature, and the signature of a tiny split in As–Fe bond distances with broken spatial inversion symmetry in a wide temperature/doping range. The former reveals a nematic state, and the latter highlights a fluctuated state of polar structure which can be appropriately called polar nematic state.

Muon spin rotation and resonant soft X-ray scattering experiments on prototype multiferroics RMn2O5 (R = Y, Sm) are used to demonstrate that the local electric displacements are driven by the spin-current (SC) mechanism. Small local electric displacements were evaluated by observing spin polarization at ligand O ions, for which implanted muons served as an extremely sensitive probe. Our results for YMn2O5 provide evidence that the spin polarization of O ions forming a spin cycloid chain with Mn spins increases in proportion to the vector spin chirality (Si x Sj ) of the Mn ions. This relationship strongly indicates that the charge transfer between O and Mn ions is driven by the SC mechanism, which leads to the ferroelectricity accompanying O spin polarization.

We investigated the multiscale characters of the crystal structure of the oxynitride perovskite LaTiO2N. While X-ray diffraction results identified the average structure as being centrosymmetric, we detected a signature of unknown structural deformation. By viewing the local structure, we unveiled the formation of a polar structure at the nanoscale.

Two carboxyl-substituted iron(II) grids, one protonated, [Fe4(HL)4](BF4)4·4MeCN·AcOEt (1), and the other deprotonated, [Fe4(L)4]·DMSO·EtOH (2), where H2L = 4-{4,5-bis[6-(3,5-dimethylpyrazol-1-yl)pyrid-2-yl]-1 H-imidazol-2-yl}benzoic acid, were synthesized. Single-crystal X-ray structure analyses reveal that both complexes have a tetranuclear [2 × 2] grid structure. 1 formed one-dimensional chains through intermolecular hydrogen bonds between the carboxylic acid units of neighboring grids, while 2 formed two-dimensional layers stabilized by π-π-stacking interactions. 1 showed spin transition between the 3HS-1LS and 1.5HS-2.5LS states around 200 K, while 2 showed spin-crossover between the 4LS and 2LS-2HS states above 300 K. A modified indium-tin oxide (ITO) electrode was fabricated by soaking the ITO in a solution of 1. The resultant electrode showed reversible redox waves attributed to the original redox processes of iron(II)/iron(III).

We report the epitaxial growth of Ca 3 SnO antiperovskite oxide films on (0 0 1)-oriented cubic yttria-stabilized zirconia (YSZ) substrates by using a conventional pulsed laser deposition (PLD) technique. In this work, a sintered Ca 3 SnO pellet is used as the ablation target. X-ray diffraction measurements demonstrate the (0 0 1) growth of Ca 3 SnO films with the antiperovskite structure and a cube-on-cube orientation relationship to the YSZ substrate. The successful synthesis of the antiperovskite phase is further confirmed by X-ray photoemission spectroscopy. These results strongly suggest that antiperovskite-oxide films can be directly grown on substrates from the target material using a PLD technique.

The field-induced antipolar-polar structural transition in an organic antiferroelectric 2-trifluoromethylnaphthimidazole crystal is investigated by performing synchrotron X-ray diffraction. The polarities of all of the hydrogen-bonded chains become parallel with each other in the presence of an external electric field. The switching is accompanied by a giant electrostriction, which provides 1 order of magnitude larger strain than the piezoelectric strain of the organic ferroelectrics: croconic acid and poly(vinylidene fluoride); however, it is comparable to those of typical commercial piezoelectric ceramics. The crystal structure analysis with electric field shows that the origin of the observed giant electrostriction can be attributed to the shear strain that emerges from the polarity switching of the hydrogen-bonded chains. The antipolar-polar structural transition in antiferroelectrics could be employed for the development of high-performance electrostrictive organic materials.

We report a synchrotron radiation X-ray diffraction study of the BiS2-layered superconductor LaO0.5F0.5BiS2. We observed superlattice reflections with the propagation vector \(\boldsymbol{q}_{\text...

We have synthesized three kinds of novel hydrogen-bonded (H-bonded) organic conductor, β′-[H3(Cat-EDO-TTF)2]X (X = ClO4, PF6, AsF6; Cat-EDO-TTF = catechol-fused ethylenedioxytetrathiafulvalene), as anion-substituted analogues of the parent BF4 salt (X = BF4). These salts are all isostructural, however, only the BF4 salt shows a phase transition, upon which the molecular arrangement and physical properties are drastically changed in cooperation with bending of the H-bond. A systematic comparison of their crystal and electronic structures disclosed that a significant chemical pressure is generated by the present anion substitution, causing differences in their physical properties and phase transition nature. Interestingly, this chemical pressure is highly anisotropic, which exclusively changes the side-by-side interactions between the Cat-EDO-TTF skeletons in the π-stacking layer. Therefore, we conclude that this unique phase transition is caused by a cooperation of the intercolumnar side-by-side interactions with the π–π intra-dimer interactions and H-bond bending.

Formamidinium [FA, HC(NH2)2+] lead iodide and its cation mixture have attracted interest as potentials in applications for efficient solar cells superior to well-known methylammonium lead iodide. W...

A new type of magnetoelectric (ME) effect was discovered in ${\mathrm{Tb}}_{1\ensuremath{-}x}{\mathrm{Gd}}_{x}{\mathrm{Mn}}_{2}{\mathrm{O}}_{5}$ in which Gd ions are substituted into ${\mathrm{TbMn}}_{2}{\mathrm{O}}_{5}$. The substitution of Gd ions increased to $x=0.5$ was found to completely suppress increases in electric polarization below $T\ensuremath{\sim}14\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, which is clearly observed in ${\mathrm{TbMn}}_{2}{\mathrm{O}}_{5}$. The electric polarization of ${\mathrm{Tb}}_{0.5}{\mathrm{Gd}}_{0.5}{\mathrm{Mn}}_{2}{\mathrm{O}}_{5}$ reappears below $T\ensuremath{\sim}14\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ in response to an external magnetic field applied along each crystallographic axis. This isotropic ME effect is in distinction from those exhibited by the $R{\mathrm{Mn}}_{2}{\mathrm{O}}_{5}$ family and by other multiferroic compounds. Resonant x-ray scattering was used to investigate the mechanism of the ME effect, and the data clearly demonstrate that this phenomenon can be attributed to competition between two different magnetic orderings. Furthermore, the magnetic-field dependence of the resonant intensity around the O $K$ edge implies that charge transfer between O and Mn ions microscopically contributes to the ME effects. These findings indicate potential new applications for multiferroic materials.

Inelastic neutron scattering was performed for an iron-based superconductor ${\mathrm{LaFeAsO}}_{0.9}{\mathrm{D}}_{0.1}$, where most of D (deuterium) replaces oxygen, while a tiny amount goes into the interstitial sites. By first-principles calculation, we characterize the interstitial sites for D (and for H slightly mixed) with four equivalent potential minima. Below the superconducting transition temperature ${T}_{\mathrm{c}}=26\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, excitations emerge in the range 5--15 meV, while they are absent in the reference system ${\mathrm{LaFeAsO}}_{0.9}{\mathrm{F}}_{0.1}$. The strong excitations at 14.5 and 11.1 meV broaden rapidly around 15 and 20 K, respectively, where each energy becomes comparable to twice the superconducting gap. The strong excitations are ascribed to a quantum rattling, or a band motion of hydrogen, which arises only if the number of potential minima is larger than two.

The charge disproportionation of Mn $3d$ and O $2p$ electronic states was investigated in two $({\mathrm{LaMnO}}_{3}{)}_{2}{({\mathrm{SrMnO}}_{3})}_{2}$ superlattices using the resonant x-ray scattering technique. The superlattices show significantly different conductivity even with the same composition. The large modulation of the Mn $3d$ electronic state was observed in the insulating sample, however the charge disproportionation and magnetic modulation of O $2p$ were shown in the semiconductive sample. It is suggested that the charge modulation appears in either Mn $3d$ or O $2p$, which is strongly related to strength of the $p\text{\ensuremath{-}}d$ hybridization, which is the main factor determining the electric conductivity in the superlattices.

Magnetic excitations in a heavily electron-doped antiferromagnet, ${\mathrm{LaFeAsO}}_{0.5}{\mathrm{D}}_{0.5}$, have been investigated using powder inelastic neutron scattering. Unlike other parent compounds of the iron-based superconductors, the magnetic excitation gap in ${\mathrm{LaFeAsO}}_{0.5}{\mathrm{D}}_{0.5}$ was not detected down to the lowest measured temperature of 4 K. This result can be understood as a result of quasi-isotropy within the $ab$ plane, which is consistent with the band calculation result that the ${d}_{xy}$ orbital plays the dominant role in the magnetism of ${\mathrm{LaFeAsO}}_{0.5}{\mathrm{H}}_{0.5}$. In addition, the intensities of the magnetic excitations in this phase are much stronger than those in nondoped LaFeAsO. Even in the paramagnetic phase, the magnetic excitation in ${\mathrm{LaFeAsO}}_{0.5}{\mathrm{D}}_{0.5}$ persists. These results corroborate recent studies showing that the electron doping enhances the localized nature in this system.

A high tolerance to oxidation of Ru nanoparticles loaded on 12CaO·7Al2O3 (C12A7) was examined by in situ X-ray absorption fine structure (XAFS). Ru nanoparticles on electron-doped C12A7 (C12A7:e–) and stoichiometric C12A7 (C12A7:O2–) are robust to oxidation, while those on Al2O3 and on MgO with Cs promoters are easily oxidized. The oxidation tolerance is higher for Ru/C12A7:e– than Ru/C12A7:O2–. The main factor of the oxidation tolerance comes from the electron donation property of C12A7:e–. C12A7:e– is an electride in which electrons serve as anions, and these anionic electrons with a low work function (2.4 eV) have a high ability to donate electrons to supporting Ru nanoparticles with a higher work function (4.7 eV). Electron transfer from C12A7:e– maintains Ru nanoparticles in the metallic state even under oxidation condition. The Ru catalysts on C12A7:e– with high oxidation tolerance can be applied to various catalytic reactions under oxygen-rich conditions, in which conventional catalysts are rapidly...

A cyanide-bridged trigonal bipyramidal [Co3Fe2] cluster shows solvent-driven reversible on/off switching of its thermally induced electron-transfer-coupled spin transition behaviour.

L12-ordered CoPt3 and L10-ordered CoPt are formed in electron-beam-deposited (Co/Pt)4 multilayer thin films with and without a Ti underlayer, respectively, on Si/SiO2 substrates by rapid thermal annealing. The crystal structures, magnetic properties, and surface morphologies of the films are investigated by grazing incidence X-ray diffraction (GI-XRD), vibrating sample magnetometer (VSM), and scanning electron microscope (SEM), respectively. In the film without a Ti underlayer, L10-ordered CoPt with an isolated round grain structure is confirmed, showing an in-plane coercivity of 2.7 kOe. In contrast, in the film with a Ti underlayer, L12-ordered CoPt3 is confirmed together with Co-rich A1-disordered CoPt, showing an in-plane coercivity of 500 Oe, which exhibits an angular-outlined continuous film structure. The three sets of experimental results from GI-XRD, VSM, and SEM coincide well with each other.

We report that the volume of an orbital-ordered Mott insulator Ca2RuO4 is purely changed by an electrical current at constant temperature and pressure. The observed giant electromechanical response...

Pollen allergy remains a big problem in contemporary societies. We have shown in previous studies that a cloth containing a special natural ore powder (CCSNOP) is effective in relieving symptoms in patients with pollen allergies. However, in that study, subjects were exposed to CCSNOP for only one hour. In the present study, CCSNOP or control (non-woven cloth, NWC) panels were placed in the bedrooms of pollen allergy patients for two weeks during the pollen dispersal season in 2018, and the effects were investigated. Twenty-one subjects were exposed to CCSNOP panels and 10 subjects were exposed to NWC panels. Our investigations showed that use of CCSNOP resulted in relief of symptoms and reduced use of therapeutics. Moreover, the ratio of eosinophil count decrease during exposure was higher in the CCSNOP group. Furthermore, a formula for measuring various cytokines and other parameters was established and clearly showed a distinction between the CCSNOP and NWC groups. In this formula, Granulocyte Macrophage colony-stimulating Factor (GM-SCF), Interleukin (IL)-12p40, Immunoglobulin (Ig) G4 and eosinophil count were extracted. These results indicated that CCNSNOP has a beneficial effect on pollen allergy patients. Future studies shall engage in long-term monitoring of pollen allergy patients who will utilize this mineral powder for at least one year.

We investigate the thickness effects on charge and magnetic orderings in Fe perovskite oxide ${\mathrm{La}}_{1/3}{\mathrm{Sr}}_{2/3}{\mathrm{FeO}}_{3}/{\mathrm{SrTiO}}_{3}$ thin films by hard x-ray and resonant soft x-ray scattering (RSXS) with changing thin-film thickness systematically. We found that the correlation lengths of the magnetic ordering along the in-plane and out-of-plane directions are comparable and proportional to the thickness, and show stronger thickness dependence than those of charge ordering. The magnetic ordered states disappear when the correlation length of magnetic ordering decreases to that of charge ordering through the intrinsic thickness effects. Surface-sensitive grazing-incident RSXS revealed that the orderings exist even in the surface region, which indicates that the observed orderings are not affected by surface effects like oxygen vacancies. Critical thickness is in 5--15 nm, which corresponds to 4--11 antiferromagnetic ordering period. This critical value seems to be common to other ferromagnetic oxide thin films.

K3Cu3AlO2(SO4)4 is a highly one-dimensional spin-1/2 inequilateral diamond-chain antiferromagnet. Spinon continuum and spin-singlet dimer excitations are observed in the inelastic neutron scattering spectra, which is in excellent agreement with a theoretical prediction: a dimer-monomer composite structure, where the dimer is caused by strong antiferromagnetic (AFM) coupling and the monomer forms an almost isolated quantum AFM chain controlling low-energy excitations. Moreover, muon spin rotation/relaxation spectroscopy shows no long-range ordering down to 90 mK, which is roughly three orders of magnitude lower than the exchange interaction of the quantum AFM chain. K3Cu3AlO2(SO4)4 is, thus, regarded as a compound that exhibits a Tomonaga-Luttinger spin liquid behavior at low temperatures close to the ground state.

New important aspects of the hydrogen-bond (H-bond)-dynamics-based switching of electrical conductivity and magnetism in an H-bonded, purely organic conductor crystal have been discovered by modulating its tetrathiafulvalene (TTF)-based molecular π-electron system by means of partial sulfur/selenium substitution. The prepared selenium analogue also showed a similar type of phase transition, induced by H-bonded deuterium transfer followed by electron transfer between the H-bonded TTF skeletons, and the resulting switching of the physical properties; however, subtle but critical differences due to sulfur/selenium substitution were detected in the electronic structure, phase transition nature, and switching function. A molecular-level discussion based on the crystal structures shows that this chemical modification of the TTF skeleton influences not only its own π-electronic structure and π-π interactions within the conducting layer, but also the H-bond dynamics between the TTF π skeletons in the neighboring layers, which enables modulation of the interplay between the H-bond and π electrons to cause such differences.

A thin film superconductor $\mathrm{B}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{L}{\mathrm{a}}_{x}\mathrm{F}{\mathrm{e}}_{2}\mathrm{A}{\mathrm{s}}_{2}$ is the first electron-doped compound of $\mathrm{BaF}{\mathrm{e}}_{2}\mathrm{A}{\mathrm{s}}_{2}$ obtained by the substitution of Ba with La within a blocking layer. By contrast, in conventional electron-doped $\mathrm{Ba}{(\mathrm{F}{\mathrm{e}}_{1\ensuremath{-}x}\mathrm{C}{\mathrm{o}}_{x})}_{2}\mathrm{A}{\mathrm{s}}_{2}$, the dopant (Co) is inserted into the conduction layer. The different shapes, or geometries, of $\mathrm{FeA}{\mathrm{s}}_{4}$ are expected in the two compounds above. However, the structure of $\mathrm{B}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{L}{\mathrm{a}}_{x}\mathrm{F}{\mathrm{e}}_{2}\mathrm{A}{\mathrm{s}}_{2}$ is investigated here because of being a thin film. To clarify the effect of the geometry, we make use of an up-to-date method to determine the atomic positions of the $\mathrm{B}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{L}{\mathrm{a}}_{x}\mathrm{F}{\mathrm{e}}_{2}\mathrm{A}{\mathrm{s}}_{2}$ thin film using synchrotron x-ray diffraction. We established that the $\mathrm{FeA}{\mathrm{s}}_{4}$ geometry in $\mathrm{B}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{L}{\mathrm{a}}_{x}\mathrm{F}{\mathrm{e}}_{2}\mathrm{A}{\mathrm{s}}_{2}$ indicates a systematic variation upon doping, which is opposite to that in $\mathrm{Ba}{(\mathrm{F}{\mathrm{e}}_{1\ensuremath{-}x}\mathrm{C}{\mathrm{o}}_{x})}_{2}\mathrm{A}{\mathrm{s}}_{2}$. However, the superconducting transition temperatures nearly coincide with each other for the same amount of dopings. The present result contrasts with a suggestion that the $\mathrm{FeA}{\mathrm{s}}_{4}$ geometry strongly influences the superconductivity in iron pnictides. Hence, we propose that the carrier density is the more important parameter than the $\mathrm{FeA}{\mathrm{s}}_{4}$ geometry and that the electronic correlation plays a significant role in the superconductivity for the electron-doped $\mathrm{BaF}{\mathrm{e}}_{2}\mathrm{A}{\mathrm{s}}_{2}$.

Two-dimensional (2D) electrides are a new concept material in which anionic electrons are confined in the interlayer space between positively charged layers. We have carried out angle-resolved photoemission spectroscopy measurements on ${\mathrm{Y}}_{2}\mathrm{C}$, which is a possible 2D electride, in order to verify the formation of 2D electride states in ${\mathrm{Y}}_{2}\mathrm{C}$. We clearly observe the existence of semimetallic ``electride bands'' near the Fermi level, as predicted by ab initio calculations, which conclusively demonstrates that ${\mathrm{Y}}_{2}\mathrm{C}$ is a quasi-2D electride with electride bands derived from interlayer anionic electrons.

For the innovation of spintronic technologies, Dirac materials, in which the low-energy excitation is described as relativistic Dirac fermions, are one of the most promising systems, because of the fascinating magnetotransport associated with the extremely high mobility. To incorporate Dirac fermions into spintronic applications, their quantum transport phenomena are desired to be manipulated to a large extent by magnetic order in a solid. We here report a bulk half-integer quantum Hall effect in a layered antiferromagnet EuMnBi$_2$, in which field-controllable Eu magnetic order significantly suppresses the interlayer coupling between the Bi layers with Dirac fermions. In addition to the high mobility more than 10,000 cm$^2$/Vs, Landau level splittings presumably due to the lifting of spin and valley degeneracy are noticeable even in a bulk magnet. These results will pave a route to the engineering of magnetically functionalized Dirac materials., Comment: 26 pages, 4 figures, 1 table

Three polymorphic forms of 6,6′-dimethyl-2,2′-bipyridinium chloranilate crystals were characterized to understand the origin of polarization properties and the thermal stability of ferroelectricity. According to the temperature-dependent permittivity, differential scanning calorimetry, and X-ray diffraction, structural phase transitions were found in all polymorphs. Notably, the ferroelectric α-form crystal, which has the longest hydrogen bond (2.95 A) among the organic acid/base-type supramolecular ferroelectrics, transformed from a polar structure (space group, P21) into an anti-polar structure (space group, P21/c) at 378 K. The non-ferroelectric β- and γ-form crystals also exhibited structural rearrangements around hydrogen bonds. The hydrogen-bonded geometry and ferroelectric properties were compared with other supramolecular ferroelectrics. A positive relationship between the phase-transition temperature (TC) and hydrogen-bond length ( ) was observed, and was attributed to the potential barrier height for proton off-centering or order/disorder phenomena. The optimized spontaneous polarization (Ps) agreed well with the results of the first-principles calculations, and could be amplified by separating the two equilibrium positions of protons with increasing . These data consistently demonstrated that stretching is a promising way to enhance the polarization performance and thermal stability of hydrogen-bonded organic ferroelectrics.

Solid-solid phase interconversion was observed in an organic conductor based on a hydrogen-bonded (H-bonded) TTF (tetrathiafulvalene) molecular unit, in which the π-stacked molecular arrangement and physical properties were dynamically changed with unexpected transformation of the H-bond unit between the planar and bent forms.

A hydrogen bond (H-bond) is one of the most fundamental and important noncovalent interactions in chemistry, biology, physics, and all other molecular sciences. Especially, the dynamics of a proton or a hydrogen atom in the H-bond has attracted increasing attention, because it plays a crucial role in (bio)chemical reactions and some physical properties, such as dielectricity and proton conductivity. Here we report unprecedented H-bond-dynamics-based switching of electrical conductivity and magnetism in a H-bonded purely organic conductor crystal, κ-D3(Cat-EDT-TTF)2 (abbreviated as κ-D). This novel crystal κ-D, a deuterated analogue of κ-H3(Cat-EDT-TTF)2 (abbreviated as κ-H), is composed only of a H-bonded molecular unit, in which two crystallographically equivalent catechol-fused ethylenedithiotetrathiafulvalene (Cat-EDT-TTF) skeletons with a +0.5 charge are linked by a symmetric anionic [O···D···O](-1)-type strong H-bond. Although the deuterated and parent hydrogen systems, κ-D and κ-H, are isostructural paramagnetic semiconductors with a dimer-Mott-type electronic structure at room temperature (space group: C2/c), only κ-D undergoes a phase transition at 185 K, to change to a nonmagnetic insulator with a charge-ordered electronic structure (space group: P1). The X-ray crystal structure analysis demonstrates that this dramatic switching of the electronic structure and physical properties originates from deuterium transfer or displacement within the H-bond accompanied by electron transfer between the Cat-EDT-TTF π-systems, proving that the H-bonded deuterium dynamics and the conducting TTF π-electron are cooperatively coupled. Furthermore, the reason why this unique phase transition occurs only in κ-D is qualitatively discussed in terms of the H/D isotope effect on the H-bond geometry and potential energy curve.

Compositionally tunable vanadium oxyhydrides Sr2VO4-xHx (x = 0 - 1) without considerable anion vacancy were synthesized by high-pressure solid state reaction. The crystal structures and their properties were characterized by powder neutron diffraction, synchrotron X-ray diffraction, thermal desorption spectroscopy, and first-principles density functional theory (DFT) calculations. The hydrogen anions selectively replaced equatorial oxygen sites in the VO6 layers via statistical substitution of hydrogen in the low x region (x < 0.2). A new orthorhombic phase (Immm) with an almost entirely hydrogen-ordered structure formed from the K2NiF4-type tetragonal phase with x > 0.7. Based on the DFT calculations, the degree of oxygen/hydrogen anion ordering is strongly correlated with the bonding interaction between vanadium and the ligands., 19 pages, 5 figures

The light-induced electron-transfer-coupled spin transition (ETCST) behaviour in a cyanide-bridged [Co2Fe2] tetranuclear complex has been investigated in detail, using magnetic susceptibility measurements, single-crystal X-ray structural analyses and X-ray absorption spectroscopy.

A systematic study of the crystal structure of a layered iron oxypnictide LaFeAsO1−xHx as a function of pressure was performed using synchrotron X-ray diffraction. This compound exhibits a unique phase diagram of two superconducting phases and two parent phases. We established that the As–Fe–As angle of the FeAs4 tetrahedron widens on the application of pressure due to the interspace between the layers being nearly infilled by the large La and As atoms. Such rarely observed behaviour in iron pnictides implies that the FeAs4 coordination deviates from the regular tetrahedron in the present systems. This breaks a widely accepted structural guide that the superconductivity favours the regular tetrahedron, albeit the superconducting transition temperature (Tc) increases from 18 K at ambient pressure to 52 K at 6 GPa for x = 0.2. In the phase diagram, the second parent phase at x ~ 0.5 is suppressed by pressure as low as ~1.5 GPa in contrast to the first parent phase at x ~ 0, which is robust against pressure. We suggest that certain spin-fluctuation from the second parent phase is strongly related to high-Tc under pressure.

Ordering and disordering electrons When a liquid is cooled rapidly, it can form a glass, a state stuck between liquid and solid. Two groups looked in detail into analogous dynamics in electronic systems. Sato et al. and Sasaki et al. studied layered organic materials with a triangular in-plane lattice. These materials can assume a state in which their charge distribution has a regular pattern—an electronic or charge crystal. When the materials were cooled rapidly, a charge glass was formed instead and then allowed to crystallize. The dynamics of crystallization showed similarities to the analogous processes in conventional glasses. Science , this issue p. 1378 , p. 1381

The switching of electric polarization induced by electric fields -a fundamental functionality of ferroelectrics- is closely associated with the motions of the domain walls that separate regions with distinct polarization directions. Therefore, understanding domain-walls dynamics is of essential importance for advancing ferroelectric applications. In this Letter, we show that the topology of the multidomain structure can have an intrinsic impact on the degree of switchable polarization. Using a combination of polarization hysteresis measurements and piezoresponse force microscopy on a uniaxial organic ferroelectric, alpha-6,6'-dimethyl-2,2'-bipyridinium chloranilate, we found that the head-to-head (or tail-to-tail) charged domain walls are strongly pinned and thus impede the switching process; in contrast, if the charged domain walls are replaced with electrically neutral antiparallel domain walls, bulk polarization switching is achieved. Our findings suggest that manipulation of the multidomain topology can potentially control the switchable polarization., 17 pages, 5 figures

In this study we have investigated dopant effects on a typical charge-orbital ordered state in a single layered manganite La0.5Sr1.5MnO4 using magnetization measurement and resonant x-ray scattering technique. We have studied how the charge-orbital ordered state is affected by the 3% substitution of Cr, Fe and Ga ions for Mn ions. It is revealed that the impurity doping suppresses the long-range charge-orbital order, in which the degree of suppression strongly depends on dopant ions, and eventually forms a phase-separated ground state between charge-orbital order and ferromagnetic states.

Geometrically frustrated spin systems often do not exhibit long-range ordering, resulting in either quantum-mechanically disordered states, such as quantum spin liquids, or classically disordered states, such as spin ices or spin glasses. Geometric frustration may play a similar role in charge ordering, potentially leading to unconventional electronic states without long-range order; however, there are no previous experimental demonstrations of this phenomenon. Here, we show that a charge-cluster glass evolves upon cooling in the absence of long-range charge ordering for an organic conductor with a triangular lattice, theta-(BEDT-TTF)2RbZn(SCN)4. A combination of time-resolved transport measurements and x-ray diffraction reveal that the charge-liquid phase has charge clusters that fluctuate extremely slowly (, 21 pages, 3 figures (supplementary information included)